Chromium-nickel steel



Patented May23, 1939- UNITED, STATES PATENT OFFICE custom-molar. STEEL l 'rederlakMBecketNewYorhandBu-ell I'ranks,NiagaraI'alls.N.Y..arllgnors No Drawing. Application July 10, me, I

Serial No.

scum.

to Eleca corporation or oi other elements, such an expedient is a relatively expensive one. Also it the nickel content of the steel is increased, for instance to 11% or 12% with about 18% chromium, in order to preserve the austenitic condition, the resulting material is not as easy to hot work as a steel of lower nickel content. Even in the absence oi columbium, an 18% chromium steel containing 11% or 12% nickel is not as readily hot when it is heated. This study also indicates that when only moderate amounts of chromium and nickel, for example, approximately 18% chromium and 8.50% nickel, are present in a steel treated 50 with columbium, the resulting material contains a substantial proportion of ferrite with the austenite, even after suitable heat treatment. Although the proportion oiaustenite can be increased by suitably increasing the nickel content oi the steel without chanting the amounts in In our prior application Serial No. 593,923 flied worked as one having a similar chromium con- February 18, 1932 we have disclosed a stainless tent and containing only 9% nickel. The extra steel containing 12% to 30% chromium; 8% to 2% or 3% nickel above the usual 9% increases 30% nickel; carbon in amounts less than 0.30%; materially the strength 01 the steel at elevated and columbium or tantalum, or both, in a subtemperatures, and it is probably for this reason is stantial amount not exceeding 10% but preierthat greater diiilculties are encountered in hot ably exceeding about ten times the carbon confabrication. Nevertheless, when columbium is tent. The primary function 01' the columbium present it is ordinarily necessary to increase the and tantalum in this steel is to inhibit loss of nickel content to secure hot worked products of corrosion resistance when the steel is held for a good quality from large ingots.

m long periods at elevated temperatures within the By the present invention we not only decrease :0 range 400- C. to 900' C. or when the steel is the cost of the steels without detracting from joined togetherby the commonly known fusion commercially valuable physical and corrosion processes 01 welding, such as gas or electric weldcharacteristics, but we also improve materially mg, their hot working properties. This result is ob- Study of these steels indicates that their cortained by the addition of manganese in certain g5 rosive resistance is preserved imder the above critical proportions. mentioned conditions because the columbium The data given in the following table illuscombines with at least mostot the carbon present trates the improvement secured by manganese and the resulting carbide distributes itseli! in the additions to the chromium-nickel steels containsteel in a manner that does not detrimentally ing columbium: o

Oompillltion (remaindc iron) mu 0 mm. J Bot working charsctcisticl Irllmlar corro- Percant Patent Percent Percen Pcosnt Percent lion tests Or Ni Mn 0 s1 Ch 18.45 3.80 0.47 0.10 as None Hot worked satisfactorily.-. Unsatisfactory. 13. 0.18 0. 0.06 0.42 0.43 cliileckedbadlyonhot work- Batidactory. isu 1m: cm 0.00 use 0.52 HOQQI without suious Batirtsctory. 40 13.41 10.10 1.10 not an ass fl tworkedsatisfactorilr statutory. 40

1733 10.00 1. 0.00 0.46 0.50 Hotworked satisfactorily"-.- Satisfactory. 18.28 7. 3.46 0. 0.48 1.08 Hot worked without serious Satisfactory.

checking.

ailect the corrosion resistance oi the material It is shown in this table that a plain 18% chromium-8% nickel steel can be easily hot worked into an article 0! good quality, but when subjected to intergranular corrosion tests, the metal disintcgrates readily; that, by the addition oi columbium the steel is rendered substantially o immune to grain boundary attack, and at the same time the hot working characteristics are detrimentally ailected; that, by increasing the nickel content the columbium-bearing chomiumnickel steel retains its resistance to grain bound- .5

ary attack, and possesses satisfactory but working characteristics; that, by the substitution of 4 several percent. manganese for nickel, a steelthat is also suitable for hot working and at the same time possesses improved resistance to intergranu lar attack is obtained; and that the incorporation of greater quantities of manganese than those used normally in the steels yields a product of improved hot working properties with satisfactory resistance to intergranular corrosion.

In its broader aspect the invention comprises an alloy steel having a chromium content between about 12% and 25%; a nickel content between 6% and 14%, a manganese content not less than about 1.50% and no more than a carbon content not exceeding 0.20%; and a columbium content not less than four times the carbon content nor more than 1% plus ten times the-carbon content. The silicon content of the steel should in most instances be that normally employed in the 18-18" steels, but under some conditions it is advantageous to permit the silicon content to rise to about 1%, the primary function of the slightly increased silicon being to protect the columbium in the steel during fusion welding. It is preferred that the steel contain between 16% and 25% chromium, at least 8% nickel, not over 0.1% carbon, not over 1.50% columbium,

between 0.40% and 1% silicon, and between 1.50% and 3% manganese. It is also preferred that the columbium content be at least ten times the carbon content.

In a preferred embodiment of the invention, the nickel content is insufficient in the absence of manganese to produce steel which can be made fully austenitic by commercial heat and mechanical treatments, but the sum of the manganese and nickel is sufllcient to make the steel fully austenitic when rolled andsuitably heat treated. In general, the sum of the manganese and nickel required to make the steel fully austenitic (when quenched from suitable temperatures), is least at about 16% to about 19% chromium, and increases with either higher or lower We claim: 1. Fully austenitic alloy steel hot worked and quenched article of manufacture composed of 16% to 25% chromium, carbon in an amount not over 0.1%; silicon in an amount not over 1%; columbium in an amount at least ten times the carbon content but not over 1.5%, the columbium serving to impart eflective resistance to intergranular deterioration at elevated temperatures but promoting an undesirable formation of ferrite during hot working; and 7% to nickel and 1.5% to 3% manganese which provide a fully austenitic structure in the quenched article without deleteriously affecting the hot working characteristics, the nickel being insufllcient to produce a fully austenitic steel if the manganese were not present; and the remainder iron.

2. Austenitie alloy steel hot worked article of manufacture composed of 16% to 25% chromium; carbon in an amount not over 0.1%, silicon in an amount not over 1%; columbium in an amount at least four times the carbon content but not chromium contents. 

